Developmental Amnesia Research Articles

Effects of level of processing but not of task enactment on recognition memory in a case of developmental amnesia

We report the performance in four recognition memory experiments of Jon, a young adult with early-onset developmental amnesia whose episodic memory is gravely impaired in tests of recall, but seems relatively preserved in tests of recognition, and who has developed normal levels of performance in tests of intelligence and general knowledge. Jon's recognition performance was enhanced by deeper levels of processing in comparing a more meaningful study task with a less meaningful one, but not by task enactment in comparing performance of an action with reading an action phrase. Both of these variables normally enhance episodic remembering, which Jon claimed to experience. But Jon was unable to support that claim by recollecting what it was that he remembered. Taken altogether, the findings strongly imply that Jon's recognition performance entailed little genuine episodic remembering and that the levels-of-processing effects in Jon reflected semantic, not episodic, memory.

Using semantic memory to boost ‘episodic’ recall in a case of developmental amnesia

We report two experiments that investigated factors that might boost 'episodic' recall for Jon, a developmental amnesic whose episodic memory is gravely impaired but whose semantic memory seems relatively normal. Experiment 1 showed that Jon's recall improved following a semantic study task compared with a non-semantic study task, as well as following four repeated study trials compared with only one. Experiment 2 additionally revealed that Jon's recall improved after acting compared with reading action phrases at study, but only if the phrases were well integrated semantically. The results provide some support for the hypothesis that Jon's 'episodic' recall depends on the extent to which he is able to retrieve events using semantic memory.

Developmental amnesia: Fractionation of developing memory systems

Study of the developmental amnesias utilizing a cognitive neuropsychological methodology has highlighted the dissociations that may occur between the development of components of memory. M.M., a new case of developmental amnesia, was identified after screening from the normal population on cognitive and memory measures. Retrospective investigation found that he was of low birthweight. M.M. had impaired semantic memory for knowledge of facts and words. There was impaired episodic memory for words and stories but intact episodic memory for visual designs and features. This forms a double dissociation with Dr S. (Temple, 1992), who had intact verbal but impaired visual episodic memory. M.M. also had impaired autobiographical episodic memory. Nevertheless, learning over repeated trials occurred, consistent with previous theorizing that learning is not simply the effect of recurrent episodic memory. Nor is it the same as establishing semantic memory, since for M.M. semantic memory is also impaired. Within reading, there was an impaired lexico-semantic system, elevated levels of homophone confusion, but intact phonological reading, consistent with surface dyslexia and raising issues about the interrelationship of the semantic system and literacy development. The results are compatible with discrete semi-independent components within memory development, whereby deficits are associated with residual normality, but there may also be an explicit relationship between the semantic memory system and both vocabulary and reading acquisition.

Developmental and Acquired Dyslexias

Marshall (1984) highlighted potential parallels between children with developmental disorders of reading and adults who had acquired reading disorders. He advocated the use of a cognitive neuropsychological framework in the investigation of children with developmental abnormalities of cognition, including those with developmental dyslexias. Developmental phonological dyslexia has been extensively described and is a pervasive disorder. The relationship between reading difficulty and phonological difficulties evident in explicit oral phonological tasks continues to be a focus for debate. Clear cases of developmental deep dyslexia have now been described and the syndrome has also been described as characterising early reading development in Williams syndrome (WS), where there are also semantic errors in other domains, including naming and receptive vocabulary and there may be a generalised difficulty with the activation of fine grain semantic specifications. In the domain of number, highly selective reading disorders characterised by high rates of semantic errors have been documented, indicating that semantic reading errors can be domain-specific. They can occur to number words despite intact ability to read Arabic numbers and they can occur to Arabic numbers and number words despite intact ability to read words in other domains. Current models of reading written words do not allow for such material-specific dissociation. Developmental surface dyslexia has also been described in a range of countries, languages and orthographies. Descriptions of cases for whom there is no phonological impairment in reading have generated contrary evidence for theories suggesting that phonological impairment underlies all developmental dyslexia. As reading develops in Williams Syndrome, phonological reading skills may improve with over-reliance on these leading to surface dyslexia. Surface dyslexia has also been reported in cases of developmental amnesia in which there are semantic memory impairments. Hyperlexia can take several forms including broad hyperdevelopment with elevated phonological reading abilities, lexico-semantic reading abilities and reading comprehension as in Turner's syndrome (TS). This advantage has early onset in school-starters. These specific modular effects do not have pervasive impact across systems but demonstrate the limitations of functional plasticity in developmental and genetic disorders. The framework Marshall (1984) outlined has provided a foundation for the development of systematic investigation of developmental disorders.

How children suffering severe amnesic syndrome acquire new concepts?

Recent studies revealed that children with developmental amnesia acquired new semantic information. However, they failed to investigate the growth of such knowledge during childhood, and they did not bring evidence concerning the putative role of residual episodic memory in semantic acquisition. This prospective study sought to clarify this issue by assessing both semantic and episodic memory in two amnesic children (RH and KF) with different neuropsychological profiles. We thus applied errorless semantic learning and vanishing cues methods, together with assessments of episodic memory using original recognition tasks within the same protocol. Results demonstrated learning and long-lasting maintenance of multicomponent concepts (comprising labels, categories and features) in both amnesic children. Importantly, episodic memory assessments revealed differential residual abilities in these children, which may account for their respective profiles of semantic acquisition. Thus, RH, who demonstrated residual episodic abilities, acquired normally. However, the learning of KF, who had a massive impairment of episodic memory, remained slower than her controls. In conclusion, even though an episodic impairment may slacken new semantic learning, our research provides new evidence for the de novo acquisition of semantic concepts in childhood amnesic syndrome and strengthens the idea that semantic learning can occur without any recruitment of episodic memory.

Memory Strength and Repetition Suppression: Multimodal Imaging of Medial Temporal Cortical Contributions to Recognition

Declarative memory permits an organism to recognize stimuli that have been previously encountered, discriminating them from those that are novel. One basis for recognition is item memory strength, which may support the perception of stimulus familiarity. Though the medial temporal lobes are known to be critical for declarative memory, at present the neural mechanisms supporting perceived differences in memory strength remain poorly specified. Here, functional MRI (fMRI) and anatomically constrained magnetoencephalography (MEG) indexed correlates of graded memory strength in the human brain, focusing on medial temporal cortex. fMRI revealed a decrease in medial temporal cortical activation that tracked parametric levels of perceived memory strength. Anatomically constrained MEG current estimates revealed that strength-dependent signal reductions onset within 150-300 ms. Memory strength appears to be rapidly signaled by medial temporal cortex through repetition suppression (activation reductions), providing a basis for the subjective perception of stimulus familiarity or novelty.

Deferred Imitation of Action Sequences in Developmental Amnesia

The aims of this study were to investigate whether patients with developmental amnesia (DA) associated with bilateral hippocampal volume reduction show an impairment in incidental nonverbal recall of action sequences, and whether the severity of this memory impairment is influenced by the sequence structure (causal vs. arbitrary). Like adult-onset cases of amnesia (McDonough, Mandler, McKee, & Squire, 1995), patients with DA did not differ significantly from their age-, sex-, and IQ-matched controls in spontaneous production of the sequences prior to modeling but recalled fewer target actions and action pairs than the control group after a 24-hour delay, independent of sequence structure. Unlike the patients with adult-onset amnesia, however, the patients with DA showed some memory for both types of sequences after a 24-hour delay. This difference in severity of memory impairment might reflect differences in extent of pathology and/or age at injury.

Developmental amnesia: a new pattern of dissociation with intact episodic memory

A case of developmental amnesia is reported for a child, CL, of normal intelligence, who has intact episodic memory but impaired semantic memory for both semantic knowledge of facts and semantic knowledge of words, including general world knowledge, knowledge of word meanings and superordinate knowledge of words. In contrast to the deficits in semantic memory, there are no impairments in episodic memory for verbal or visual material, assessed by recall or recognition. Lexical decision was also intact, indicating impairment in semantic knowledge of vocabulary rather than absence of lexical representations. The case forms a double dissociation to the cases of Vargha-Khadem et al. [Science 277 (1997) 376; Episodic memory: new directions in research (2002) 153]; Gadian et al. [Brain 123 (2000) 499] for whom semantic memory was intact but episodic memory was impaired. This double dissociation suggests that semantic memory and episodic memory have the capacity to develop separately and supports models of modularity within memory development and a functional architecture for the developmental disorders within which there is residual normality rather than pervasive abnormality. Knowledge of arithmetical facts is also spared for CL, consistent with adult studies arguing for numeracy knowledge distinct from other semantics. Reading was characterised by difficulty with irregular words and homophones but intact reading of nonwords. CL has surface dyslexia with poor lexico-semantic reading skills but good phonological reading skills. The case was identified following screening from a population of normal schoolchildren suggesting that developmental amnesias may be more pervasive than has been recognised previously.

Developmental amnesia and its relationship to degree of hippocampal atrophy

Two groups of adolescents, one born preterm and one with a diagnosis of developmental amnesia, were compared with age-matched normal controls on measures of hippocampal volume and memory function. Relative to control values, the preterm group values showed a mean bilateral reduction in hippocampal volume of 8-9% (ranging to 23%), whereas the developmental amnesic group values showed a reduction of 40% (ranging from 27% to 56%). Despite equivalent IQ and immediate memory scores in the two study groups, there were marked differences between them on a wide variety of verbal and visual delayed memory tasks. Consistent with their diagnosis, the developmental amnesic group was impaired relative to both other groups on nearly all delayed memory measures. The preterm group, by contrast, was significantly impaired relative to the controls on only a few memory measures, i.e., route following and prospective memory. We suggest that early hippocampal pathology leads to the disabling memory impairments associated with developmental amnesia when the volume of this structure is reduced below normal by approximately 20-30% on each side. Whether this is a sufficient condition for the disorder or whether abnormality in other brain regions is also necessary remains to be determined.

Developmental amnesia: effect of age at injury.

Hypoxic-ischemic events sustained within the first year of life can result in developmental amnesia, a disorder characterized by markedly impaired episodic memory and relatively preserved semantic memory, in association with medial temporal pathology that appears to be restricted to the hippocampus. Here we compared children who had hypoxic-ischemic events before 1 year of age (early group, n = 6) with others who showed memory problems after suffering hypoxic-ischemic events between the ages of 6 and 14 years (late group, n = 5). Morphometric analyses of the whole brain revealed that, compared with age-matched controls, both groups had bilateral abnormalities in the hippocampus, putamen, and posterior thalamus, as well as in the right retrosplenial cortex. The two groups also showed similar reductions (approximately 40%) in hippocampal volumes. Neuropsychologically, the only significant differences between the two were on a few tests of immediate memory, where the early group surpassed the late group. The latter measures provided the only clear indication that very early injury can lead to greater functional sparing than injury acquired later in childhood, due perhaps to the greater plasticity of the infant brain. On measures of long-term memory, by contrast, the two groups had highly similar profiles, both showing roughly equivalent preservation of semantic memory combined with marked impairment in episodic memory. It thus appears that, if this selective memory disorder is a special syndrome related to the early occurrence of hypoxia-induced damage, then the effective age at injury for this syndrome extends from birth to puberty.

Dissociations in cognitive memory: the syndrome of developmental amnesia.

The dearth of studies on amnesia in children has led to the assumption that when damage to the medial temporal lobe system occurs early in life, the compensatory capacity of the immature brain rescues memory functions. An alternative view is that such damage so interferes with the development of learning and memory that it results not in selective cognitive impairments but in general mental retardation. Data will be presented to counter both of these arguments. Results obtained from a series of 11 amnesic patients with a history of hypoxic ischaemic damage sustained perinatally or during childhood indicate that regardless of age at onset of hippocampal pathology, there is a pronounced dissociation between episodic memory, which is severely impaired, and semantic memory, which is relatively preserved. A second dissociation is characterized by markedly impaired recall and relatively spared recognition leading to a distinction between recollection-based versus familiarity-based judgements. These findings are discussed in terms of the locus and extent of neuropathology associated with hypoxic ischaemic damage, the neural basis of 'remembering' versus 'knowing', and a hierarchical model of cognitive memory.

Closing Comments

Closing Comments

Developmental amnesia associated with early hypoxic-ischaemic injury.

We recently reported on three young patients with severe impairments of episodic memory resulting from brain injury sustained early in life. These findings have led us to hypothesize that such impairments might be a previously unrecognized consequence of perinatal hypoxic-ischaemic injury. Neuropsychological and quantitative magnetic resonance investigations were carried out on five young patients, all of whom had suffered hypoxic-ischaemic episodes at or shortly after birth. All five patients showed severe impairments of episodic memory (memory for events), with relative preservation of semantic memory (memory for facts). However, none had any of the major neurological deficits that are typically associated with hypoxic-ischaemic injury, and all attended mainstream schools. Quantitative magnetic resonance investigations revealed severe bilateral hippocampal atrophy in all cases. As a group, the patients also showed bilateral reductions in grey matter in the regions of the putamen and the ventral part of the thalamus. On the basis of their clinical histories and the pattern of magnetic resonance findings, we attribute the patients' pathology and associated memory impairments primarily to hypoxic-ischaemic episodes sustained very early in life. We suggest that the degree of hypoxia-ischaemia was sufficient to produce selective damage to particularly vulnerable regions of the brain, notably the hippocampi, but was not sufficient to result in the more severe neurological and cognitive deficits that can follow hypoxic-ischaemic injury. The impairments in episodic memory may be difficult to recognize, particularly in early childhood, but this developmental amnesia can have debilitating consequences, both at home and at school, and may preclude independent life in adulthood.

Metabolic profile of various neural cells: A basis for interpreting 1H NMR brain spectra in vivo

Paillard [Paillard J. Réflexions sur l’usage du concept de plasticité en Neurobiologie. J Psychol Norm Pathol 1976;1:33–47] defined adaptive plasticity as the capacity of the system to change its own structure and expand its behavioural repertoire. We review the literature on brain damage patients, in whom, adaptive plasticity was observed via neuropsychological and functional neuroimaging examinations. Attentional and memory system alterations and some resulting changes considered as compensatory mechanisms are commented. We have selected a single case presenting with developmental amnesia [Vargha-Khadem F, Gadian DG, Watkins KE, Connelly A, Van Paesschen W, Mishkin M. Differential effects of early hippocampal pathology on episodic and semantic memory. Science 1997;277(5324):376–80; Maguire EA, Vargha-Khadem F, Mishkin M. The effects of bilateral hippocampal damage on fMRI regional activations and interactions during memory retrieval. Brain 2001;124(Pt 6):1156–70] and several groups of multiple sclerosis patients studied recently [e.g. Mainero C, Pantano P, Caramia F, Pozzilli C. Brain reorganization during attention and memory tasks in multiple sclerosis: insights from functional MRI studies. J Neurol Sci 2006;245(1/2):93–8; Morgen K, Sammer G, Courtney SM, Wolters T, Melchior H, Blecker CR, et al. Distinct mechanisms of altered brain activation in patients with multiple sclerosis. Neuroimage 2007;37(3):937–46; Nebel K, Wiese H, Seyfarth J, Gizewski ER, Stude P, Diener HC, et al. Activity of attention related structures in multiple sclerosis patients. Brain Res 2007;1151:150–60]. Convergence evidence via the two approaches – neuropsychological and functional fMRI – was shown as functional and structural brain plasticity was demonstrated in the selected works. Some common characteristics of brain plasticity emerge from this review independently of the neurological conditions we reviewed.

Le fétichisme de la langue

Language fetishism Language fetishism is based upon double developmental amnesia : amnesia in regard to the social conditions which produce linguistic distinction as well as the belief in the absolute value and entire legitimacy of this "natural distinction" ; amnesia in regard to the social conditions which generate conform producers and recepters and, by this, disregard of the system of differences which is fundamental to the profits of distinction offered by the mastery of the legitimate language. Linguistics mask the question of the social conditions of obtaining legitimate competence in language. This does not mean however that linguistics do not reply to this question. One of two explanations is usually offered : either this competence is described as common "treasure" which can be appropriated by particular person under unspecified conditions ; or else under the cover of the criteria of "grammaticality", linguistic competence becomes that which is measured only by grammarians. Linguistics tend to reduce the universe of different utilizations to that of only one particular utilization of language the "correct utilization" ; that is to say, the dominant utilization as well as the utilization to which the dominant members of society put this language. Because this language is not clearly recognized as that of the dominant members of society it becomes all the more legitimate. In this way linguistics incorporate within scientific theory the social operation of universalizing the particular and naturalizing the arbitrary which is the source of legitimacy of the "correct utilization". Thus this particular means of expression is seen to be universally accessible and required. The social conditions of legitimate language production are fundamental in understanding the properties and specific effects of language. Moreover, it is necessary to understand the social mechanisms which bring about the same effects by guaranteeing the reproduction of the structure of distribution between classes of the knowledge and the use of the legitimate language. These same mechanisms guarantee at the same time the reproduction of the market in which legitimate linguistic products receive their full value and also guarantee the need for these written or spoken products and the need for those who produce them : writers (private or public) or speakers.